Calculating grounding chassis wire length and gauge for a frequency range

Discussion in 'General Electronics Chat' started by jaspar, Aug 28, 2008.

  1. jaspar

    Thread Starter New Member

    Aug 26, 2008
    I have a component and there is no chassis grounding to ground it. The only way to ground this component is to use electircal wire through the connector and attach it to an external ground.

    Now I need to find out how long the chassis wire and how big the wire gauge should be to meet the impedance value of 2.5 milli ohms for the frequency range of 100kHz to 2GHz.

    Assuming for a copper 22 gage wire at 20'C:

    For the DC resistance I know that it is
    Resistance = Resistivity * Length / Area.

    How about for the AC part?
    Is it: Impedance Z = 2*pi*F*L + 1/(2*pi*F*C) + R,

    where F is the frequency, L is the inductance and C is the capacitance.

    How do I calculate the L and the C? Actually is the C even needed since the Frequency is high that component will just go to 0 right?

    Any help would be appreciated.
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    At the upper part of your frequency range, the current is going to concentrate on the surface of the conductor (skin effect). You really need a conductor with many tiny wires to minimize this effect. European ground wires are made with many small diameter conductors for this reason.

    But at 2 GHz, everything is inductive, and stray capacitance is hard to manage. A run of any length is going to be just about impossible to calculate. The chassis itself will make a real problem thanks to circulating currents. If it is grounded through a solid wire, that will also be a problem, as that inductance will be added to the total, with skin effect affecting that inductance.

    What is the component, and why does it need a chassis ground?